Compared to core or open biopsies, fine needle aspirates (FNA) are a quick and relatively safe method of biopsy to provide samples for evaluation of clinically suspicious mass lesions. FNA are often a first step in evaluating whether a patient has a malignancy. Routine collections during FNA include paired smears (Diff-Quick and H&E) and cell block (clot block or cell disk). Each collection is from a single pass or aspiration. The paired smears are routinely performed on most of the passes to rapidly evaluate the morphology of the suspicious lesion. The cell block is used to process the specimen in a manner to allow for ancillary testing. For example, the cell block can be used to evaluate immunohistochemistry, FISH, PCR and the like, as well as to assess morphology. The morphology of blocks may be diagnostically complimentary in that they often provide more data with regard to the architectural arrangement of cells compared to smears. The evaluation of cells from FNAs typically employs very limited cell material. It is a known problem that the quality of the cell block can deteriorate compared to paired cell smears from the same procedure. Unfortunately, this deterioration can impair additional, sometimes confirmatory, testing or analysis that can be carried out on the specimen. This can result in an inconclusive diagnosis typically requiring additional diagnostic procedures at increased risk and/or cost to the patient and may delay specific therapy.
In the past, the cell blocks have been prepared using samples that are expelled onto glass slides and placed in formalin within a short time frame. The cell block is allowed to “clot” together to make a relatively solid specimen that can be processed to make formalin-fixed paraffin embedded (FFPE) tissue samples. This cell block preparation process can result in undue cell loss resulting in decreasing (and sometimes no) cell yields in the FFPE tissue samples.